This invention concerns a method for the purification of alkylene carbonates, especially high purity alkylene carbonates.
Alkylene carbonates are well known materials that have been produced commercially for decades. Alkylene carbonate may be manufactured by a variety of methods. One such method is described in U.S. Pat. No. 2,773,070 (1956). Some applications of alkylene carbonate demand use of very high purity products. For example, when alkylene carbonates are used as solvents for electrolyte salts in lithium batteries, the alkylene carbonate preferably contain essentially no impurities (e.g., glycol less than 20 parts per million (xe2x80x9cppmxe2x80x9d) and very low water amounts (also less than 20 ppm). In the past, such purification was accomplished, for instance, by treatment by distillation; however, the impure streams from the distillation tower(s), which may constitute up to 50 percent of the effluent from the carbonate reactor, are typically considered useless byproducts that are destroyed.
U.S. Pat. No. 6,156,160 (xe2x80x9cthe ""160 patentxe2x80x9d), the entire contents of which are herein incorporated by reference thereto, describes a process for the production and purification of alkylene carbonates. In one respect, the ""160 patent teaches a process useful for the manufacture of alkylene carbonate, comprising: contacting carbon dioxide, an alkylene oxide, and a carbonation catalyst in a reaction zone to produce a crude reactor effluent; subjecting the crude reactor effluent to low temperature evaporation to form an evaporator overhead containing alkylene carbonate and an evaporator bottoms stream containing the catalyst, and recycling the evaporator bottoms stream to the reaction zone, removing any light components present in the evaporator overhead to form a second evaporator overhead and recycling the light components to the reaction zone; distilling the second evaporator overhead to form a first distillation overhead stream and a first distillation bottoms stream containing alkylene carbonate, and recycling the first distillation overhead stream to the reaction zone; distilling the first distillation bottoms stream to form a second distillation overhead stream and a second distillation bottoms stream and recycling the second distillation bottoms stream to the reaction zone; distilling the second distillation overhead stream to form a third distillation overhead stream and a third distillation bottoms stream and recycling the third distillation overhead stream to the reaction zone; distilling the third distillation bottoms stream to form a fourth distillation overhead stream containing purified alkylene carbonate and a fourth distillation bottoms stream, and recycling the fourth distillation bottoms stream to the reaction zone. In another respect, the ""160 patent provides a process useful for the manufacture of an alkylene carbonate, comprising: distilling a first stream containing an alkylene carbonate in a purity of about 99 percent or more to form a first bottoms stream containing alkylene carbonate at a purity greater than the purification stream and an first overhead stream containing alkylene carbonate at a purity greater than the purification stream, and introducing the first overhead stream to an alkylene carbonate reactor; distilling the first bottoms stream to form a second overhead stream containing high purity alkylene carbonate and a second bottoms stream, and recycling the second bottoms stream to the alkylene carbonate reactor. In another respect, the ""160 patent teaches a process useful for the manufacture of an alkylene carbonate, comprising: contacting carbon dioxide, an alkylene oxide, and a carbonation catalyst in a reactor to produce a crude reactor effluent; subjecting the crude reactor effluent to low temperature evaporation to form an evaporator overhead containing alkylene carbonate and an evaporator bottoms stream containing the catalyst, and recycling the evaporator bottoms stream to the reactor, removing any light components present in the evaporator overhead to form a second evaporator overhead and recycling the light components to the reactor; distilling the second evaporator overhead to form a first distillation overhead stream and a first distillation bottoms stream containing alkylene carbonate, and recycling the first distillation overhead stream to the reactor; distilling the first distillation bottoms stream to form a second distillation overhead stream and a second distillation bottoms stream and recycling the second distillation bottoms stream to the reactor; distilling the second distillation overhead stream in a distillation column to form a third distillation overhead stream, a high purity middle fraction having a purity of at least 99.99% and a third distillation bottoms stream, withdrawing the middle fraction from the column, and recycling the third distillation overhead stream and the third distillation bottoms stream to the reactor. In yet another respect, the ""160 patent provides a process useful for the manufacture of ethylene carbonate, comprising: contacting carbon dioxide, an ethylene oxide, and a carbonation catalyst in a reactor to produce a crude reactor effluent; subjecting the crude reactor effluent to low temperature evaporation to form an evaporator overhead containing ethylene carbonate and an evaporator bottoms stream containing the catalyst, and recycling the evaporator bottoms stream to the reactor, removing any light components present in the evaporator overhead to form a second evaporator overhead and recycling the light components to the reactor; subjecting the second evaporator overhead to a second low temperature evaporation to form a less pure fraction and a more pure fraction, and recycling the less pure fraction to the reactor; and either: (1) distilling the more pure fraction in a distillation column to form a less pure overhead fraction, a high purity middle fraction having a purity of at least 99.99% and a less pure bottoms fraction, withdrawing the middle fraction from the column, and recycling the less pure overhead fraction and the less pure bottoms fraction to the reactor, or (2) distilling the more pure fraction to form a distillation overhead stream and a distillation bottoms stream and recycling the distillation overhead stream to the reactor; distilling the distillation bottoms stream to form a second distillation overhead stream containing purified alkylene carbonate having a purity of at least 99.99% and a second distillation bottoms stream, and recycling the second distillation bottoms stream to the reactor.
While it is believed to be representative of the current state of the art with respect to the manufacture and purification of alkylene carbonates, the ""160 patent is not without its drawbacks, most notably the amount of overall energy consumed during alkylene carbonate production, and the final product yield. The present inventors have recognized that a need exists to further increase the efficiency of the alkylene carbonate production and purification process.
The present invention provides process for providing a purified alkylene carbonate from a crude alkylene carbonate, comprising the steps of: a) providing a crude alkylene carbonate by reacting carbon dioxide with an alkylene oxide in a reactor in the presence of a suitable catalyst; b) subjecting the crude alkylene carbonate to evaporation in a first evaporator to form a first evaporator overhead containing alkylene carbonate and a first evaporator bottoms stream containing the catalyst, and recycling the first evaporator bottoms stream to the reactor; c) subjecting the first evaporator overhead to evaporation in a second evaporator to form a second evaporator overhead containing light components present in the first evaporator overhead and recycling the light components to the reactor; and d) contacting the bottoms stream from the second evaporator with carbon to form a high purity alkylene carbonate product. Advantageously, the inventive process may be carried out using conventional equipment.